The present invention relates to a method of continuous thermal treatment of a textile product web as well as to a dryer for performing the method.
For continuous thermal treatment of a textile product web, such as drying, drying and/or fixing, it is known to bring the product web in several successive steps in contact with a treatment gas of a corresponding temperature. Such a thermal treatment can be performed in a drying and fixing device disclosed in the German patent document DE A 25 45 440, in particular for textile webs which are fed there by their width.
A dryer, such as a tender dryer, has fields which are arranged one after the other and corresponds to the treatment stages. In each field or in each stage, the treatment gas is guided in a circulating process.
In many cases, heated air is used as the treatment gas. It is also known to use steam as the treatment gas, as disclosed for example in the German patent document DE-A 195 46 344.
A method which utilizes both the advantages of a treatment with heated air and also a treatment with steam, and a corresponding dryer, are disclosed in the German patent document DE-B 95 26 17. In this process for drying of continuous material webs, the product is treated in successive portions of the drying machine alternatingly with heated air and overheated steam. The portions of the drying machine can include several chambers which are also the above mentioned fields. For subdividing the treatment into these portions, the machine is subdivided for example by partitions into successive treatment zones with air or steam as a drying medium.
These processes have however the disadvantage that for different application cases a new dryer is needed. At least, the partitions must be displaced.
Accordingly, it is an object of the present invention to provide a method for continuous thermal treatment of a textile product web which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated in a method which includes the steps of bringing a product web in contact with a treatment gas guided in a circulating process, introducing a product web into a steam portion having one or several steam stages in which heat steam is used as a treatment gas, introducing the product web into a steam-air portion which has one or several stages and hot steam and heated air as a treatment gas, passing the product web first through the steam portion and subsequently through the steam air portion, providing an exchange of the treatment gas between the steam stages and the stages, adjusting a relative moisture of the hot steam of the steam stages of the steam portion to the value zero, and performing the adjusting by measuring relative moistures of a first and a last steam stage and changing discharge gas quantities of the first or second steam stages and one further stage.
It is another object of the present invention to provide a dryer which can implement the inventive method.
In keeping with these objects, a dryer is proposed which has a steam-tight housing through which a product web is transportable; at least two successively arranged fields each provided with a circulating device for a treatment gas; moisture sensors arranged in first fields and in at least one rear field; a discharge conduit provided with an adjusting arrangement and arranged at least in a first or a second field and in at least one further field correspondingly; a switching unit through which at least two of said moisture sensors are connected; said switching unit being connected with at least one adjusting device.
When the method is performed and the dryer is designed in accordance with the present invention, various application cases can be realized without significant conversion expenses of the dryer.
In the inventive method for continuous thermal treatment of a textile product web, the product web passes first through one or several steam portions which have steam stages, in which hot steam is used as a treatment gas, and subsequently it passes through one or several air portions which have steam and in which steam and in which hot steam and heated air are used as the treatment gas. Subsequently to the steam-air portion, it can pass in some cases through an air portion with one or several stages in which it is brought into contact with heated air. The number of the steam stages of the steam portion are selected in dependence on the treatment process, wherein for drying there is a tendency for rather more steam stages for drying and fixing and in some cases less steam stages, and for fixing for example only one steam stage is utilized.
A treatment with steam has the advantage that the product web is heated very fast to a temperature of up to 100xc2x0 C.
With the steam portion during a thermal treatment of a product web, the shrinkage which requires a certain moisture and is enhanced by high temperature of the product web is facilitated. The product web which has approximately input moisture and is heated to 100xc2x0 C. is dried at this temperature. It has during shrinkage this high temperature at a moisture of approximately 30%. If the treatment gas to the contrary has a lower steam content, then the product web during the drying has a lower cooling limiting temperature corresponding to the steam content. An improved shrinkage during drying has for example an additional shrinkage treatment such as tumbling.
In the inventive method the relative moisture or in other words the volume of the water steam with respect to the volume of the treatment gas is adjusted to the steam stages of the steam portion to the value 1. A relative moisture with the value 1 corresponds to a treatment gas which has up to 100 of saturated, mainly overheated water steam, identified as a hot steam. In guarantees a fast warming of the product web to 100xc2x0 C.
In principle it is known to adjust the moisture of the treatment gas. In the above mentioned German patent document DE-A 25 45 440 it is described that during drying the steam content which corresponds to the relative moisture is held constant by controlling the fresh air supply in the individual fields. In addition a temperature sensor regulates the discharge air quantity. A steam content of 100xc2x0 C. adjusted by the regulation of the fresh air supply; is basically not possible. Each fresh air supply would reduce the steam content to the value under 100%. A fresh air supply in the fields operating with hot steam is excluded because of the condensation danger.
This document also discloses a simplifying embodiment, in which during drying the discharge airfans which determine the discharge air quantity are controlled by a steam content sensor. The discharge air fans are connected with several fields. The disadvantage of this method is that the steam content can be regulated only together for the fields connected to one discharge air fan. Thereby the number of the steam fields and correspondingly the number of the steam stages are fixed.
In accordance with the present invention, the relative moisture of the hot steam of the steam stages of the steam portion is adjusted to the value 1, in that the moisture of the treatment gas, in other words the hot steam, of the first and the last steam stage is measured and the discharge gas of the first or the second steam stage and one further stage is changed. This method has the advantage that independently from the number of the steam stages, only two discharge gas quantities are changed.
In a dryer which is suitable for performing the method, corresponding discharge gas conduits only for two fields are needed. It is important that in accordance with the present invention in this open process, or in other words with an exchange of a treatment gas between the stages and thereby between the fields, the discharge gas is discharged only in two fields, while the quantities are changed due to the measured relative moisture.
When compared with a discharge gas control of each stage, with the inventive method both the structural expenses and the operational expenses are substantially reduced. The temperature of the treatment gasses guided in the circulation process are adjusted separately in individual stages.
In accordance with another feature of present invention, the relative moisture of the steam stage is adjusted to the value 1 and relative moisture of all remaining stages is adjusted to a predetermined value in that the relative moisture of the steam stages and at least one further stage are measured and the discharge quantity of the steam stage and at least one further stage are changed. In this process the steam portion includes only one steam stage. This is suitable especially well for fixing. The for example dry product web is heated in the first stage formed as the steam stage very fast to 100xc2x0 C., so that subsequently in steam-air stages or air stages it can be further heated to the temperature required for fixing for example of the applied paint.
For a measurement of two relative moistures, namely of the steam stage and a further stage and changing of two discharge gas quantities, namely of the steam stage and a further stage, which can be different from the stage in which the moisture is measured, the relative moisture of the product web is adjusted to the value 1 and the relative moisture of all other stages is adjusted to predetermined values. This method makes possible with relative expenses the adjustment of moisture in all treatment stages.
In accordance with a further embodiment of the process, the steam portion includes at least three steam stages. Two and more steam stages are especially well for drying, and drying and fixing. In this method additionally the moisture of a steam-air stage is measured and additionally the discharge gas quantity of a further steam stage or a further stage is changed. This method makes possible the adjustment of moisture in all stages with at least two steam stages by three moisture measurements and three changes of the discharge gas quantities.
In accordance with a further feature of the present invention, the discharge gas quantities of the first and the second steam stage and one further stage are changed. The change of the discharging gas quantities of the successive stages has the structural advantage that the discharge gas conduits of the corresponding fields of a dryer are arranged one after the other and for example only one joint discharge gas fan is required.
In accordance with another feature of the present invention a change of the discharge gas quantity of the last stage guarantees that also, up to the last stage, the moisture of the stages can be adjusted to the predetermined value. The last field which corresponds to the last stage of a dryer is often better accessible than the front fields.
In accordance with still a further feature of the present invention, from structural and operational reasons, similarly as in the case of both first stages, it is of advantage when the discharge gas quantities of both last stages arranged one after the other are changed. In a still further embodiment of the present invention also four relative moistures can be measured and four discharge gas quantities can be changed. This is of advantage, the longer is the treatment, or in other words more stages are available, and the more accurate the relative moistures are adjusted for efficient thermal treatment. In the inventive method up to 80% of the treatment stages can be formed as steam stages. This provides for a flexibility of the method.
In a dryer which is suitable for the method of the present invention, in all fields or in the first fields, such as the fields which are operated as steam fields, and in at least one of the rear fields, moisture sensors are arranged. The moisture sensors have each a measuring unit in the interior of the field and a measuring device connected with it and located outside of the field. The first and second field and a rear field have correspondingly a discharge conduit provided with an adjustment device. An adjustment device includes for example a flap integrated in the discharge gas conduit and connected to an adjusting unit or a regulator. Depending on which of the first fields are used as steam fields, the moisture sensors are connected through the switching unit with the adjusting devices of the discharge gas conduits. The first and/or last moisture sensors can be also directly connected with the adjusting devices of the discharge gas conduits, such a dryer can operate with one, two or more steam fields, which makes possible a great number of various methods.
For performing the method it is advantageous to make possible measurements of the relative moisture of the last steam stages. This is performed in accordance with the another feature of the present invention by the moisture sensors of all first fields or in other words all possible steam fields connected with the switching movement. The moisture sensor of the first field can be connected directly with the adjusting device of the discharge gas conduit of the first field.
In accordance with still a further feature of the present invention, moisture sensors are arranged in all of the fields. It increases the flexibility of the dryer and the accuracy, of which the moisture of the stages can be adjusted.
In a further feature of the present invention, all moisture sensors are connected to the switching unit and is connected with the adjusting devices so that it is possible to provide a central, in some cases computerized control of the thermal treatment in the dryer.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.